Diabetes refers to a condition with abnormally elevated glucose concentration in blood (plasma glucose level), and is one of the important risk factors of arteriosclerotic diseases such as ischemic cardiac diseases and the like, in addition to diabetic microangiopathy.
Therefore, it is required to improve life style as well as control the plasma glucose level to an appropriate level by taking an antidiabetic drug.
At present, various antidiabetic drugs have been marketed and used in clinical situations. However, no single pharmaceutical agent is capable of sufficiently improving the complicated pathology of diabetes, and plural pharmaceutical agents are used in combination for diabetes treatment.
A representative concomitant drug for diabetes treatment is a sulfonylurea (hereinafter sometimes to be referred to as SU) agent. However, since SU agents have a risk of causing hypoglycemia, a particular attention is required when using plural pharmaceutical agents in combination. In addition, a long-term use of SU agent is feared to cause exhaustion of β-cell.
In recent years, a highly increased risk of arteriosclerotic diseases due to duplicative development of plural risk factors including abnormal glucose metabolism, abnormal lipid metabolism, obesity, hypertension and the like has been noted. This pathology involving plural risk factors attracts attention as “metabolic syndrome” or “multiple risk factor syndrome”. With regard to this pathology, a treatment of hyperlipidemia, hypertension and obesity is required in addition to the control of plasma glucose level. In this pathology, moreover, thrombus may be easily developed due to the increased blood viscosity. Hence, a pharmaceutical agent suppressing thrombus formation, i.e., an antiplatelet drug or an anticoagulant, may also be used in combination.
Glucagon-like peptide-1 (hereinafter sometimes to be referred to as GLP-1) and glucose-dependent insulinotropic peptide (hereinafter sometimes to be referred to as GIP), which are secreted from the gastrointestinal tract after a meal, have a strong insulin secretagogue effect. However, since GLP-1 and GIP are degraded by dipeptidyl peptidase IV (hereinafter sometimes to be referred to as DPP-IV), they may fail to exhibit the effect sufficiently in the living body.
A DPP-IV inhibitor promotes insulin secretion by suppressing degradation of GLP-1 and GIP, and shows a hypoglycemic effect. Thus, it is under development as a therapeutic drug for type 2 diabetes (see non-patent reference 1).
Moreover, a treatment method attempting to control plasma glucose by combining a DPP-IV inhibitor and other antidiabetic drug is known (see patent references 1, 2). Furthermore, a recent result has documented clinical studies of plasma glucose control by a combination of a DPP-IV inhibitor LAF237 and metformin (see non-patent reference 2).
However, all of these combinations are between a particular compound having a DPP-IV inhibitory effect and other antidiabetic drug, with no specific description of a combination of 3-{(2S,4S)-4-[4-(3-methyl-1-phenyl-1H-pyrazol-5-yl)piperazin-1-yl]pyrrolidin-2-ylcarbonyl}thiazolidine, a salt of the compound with an organic or inorganic mono- or di-basic acid or a solvate thereof, as a DPP-IV inhibitor, and other antidiabetic drug, and a therapeutic effect on diabetes afforded by the combination is not known at all.    patent reference 1: WO01/052825    patent reference 2: WO01/097808    non-patent reference 1: Drucker D J, Expert Opin Investig Drugs 2003, 12: 87-100    non-patent reference 2: Ahren B et al., Diabetes Care. 2004, 27:2874-80